Direct current transformer



1939- M. 1. TOPALOV 2,164,964

DIRECT CURRENT TRANSFORMER Filed Au 10, 1956 F/gJ. L, g

IN VE/V TOR Patented July 4, 1939 UNITED STATES PATENT OFFICE 8 Claims.

My invention relates to apparatus for the conversion, inversion,rectification and/or transformation of electrical currents.

' It is an object of my invention to provide electrical currenttransforming apparatus comprising an improved commutator of a simplifiedconstruction which also provides for improved capacity, wave form andphasing.

The invention itself, however, both as to its organization and itsoperation, together with additional objects and advantages thereof willbest be understood from the following description, when readinconnection with the accompanying drawing, in which: I

Figure 1 is a side elevation view of a polyphase converter-rectifier,with associated circuit con- 'other embodiment of my converter; and

Figure 6 is a sectional view taken along line 66 thereof.

Referring more specifically to Figures 1, 2, 3 and 4 of the drawing, myimproved current changing or transforming apparatus comprises animproved commutator construction consisting of a plurality ofelectrically conductive elements I, 2, 113, 2B of cylindricalconformations of different diameters mounted on a rotatable shaft 3 inconcentric spaced apart relation with any suitable insulation material Sdisposed therebetween. The cylindrical conductive elements are ofdifierent lengths axially and are arranged in progressively projectingrelation, with the longest cylindrical element adjacent the shaft.

A pair of slip rings 4 and 5 are supportedon the adjacent ends of theshorter cylindrical elements I and 2, and a second pair of slip rings 43and 5B are supported on the adjacent ends of the longer cylindricalelements. The two slip rings of each pair of rings are preferably ofequal diameters, and the rings may be supported in axially spacedrelations for conveniently en- Figure 5 is a side elevational Viewshowing angaging stationary brushes 6, 1, 6B and 7B, as shown in Figure1.

From the opposite ends of the shorter pair of cylindrical elements I and2, a pair of annular flanges F extend in axially spaced apart relation,as shown in Fig. 2. The outer rims of the annular flanges F carrycontact segments 8 and 9 extending in alternately spaced relationdisposed equidistantly about one or several circular paths to define acontact drum. The contact drum so formed is engaged by a plurality ofspaced stationary brushes 25A, 25B, 25C, 26A, 26B and 260, shown inFigure 4. Similarlyfrom the opposite ends of the longer pair ofcylindrical elements IB and 2B, spaced annular flanges F extend tosupport contact segments 83 and 9B in alternately spaced relation forsimilarly forming a smaller contact drum having one or several circularpaths engaged by a plurality of spaced brushes, such as the brushes 23A,23B, 23C and 24A, 24B and 240 shown in Figure 3.

The areas of the contacting surfaces of the segments 8, 9, 8B and 9B aremade proportioned to the amplitude of the current in the parallelcircuits through the commutator. Also, as may be seen in Figure 1, theshape of the contacting surface of each segment is such it has a maximumcontacting area in the middle and is tapered at both the leading andlagging ends in the direction of rotation, effecting a desired increaseor decrease in contact area with the engaging brushes, increasing ordecreasing by this action gradually the current density, and providingfor the desired proportions of the sinewave curve of alternations. Thebrushes are made a little shorter than the length of the space betweenthe contact segments to prevent short circuiting. 'The dimensions ofdifferent parts of the drums are proportionalto the current andinversely proportional to the voltages to be applied.

Figures 1, 2, 3 and 4 show my improved 'device utilized in a system fordirect current transformation. For this purpose the brushes 6B and 1Bare connected by suitable conductors with the available source of directcurrent, which may be service line conductors Li and L2, whereby theelements IB and 2B are provided with constant and opposite polarity, andthe associated contact drum comprises a series of oppositely chargedcontact segments. As shown, the brushes 6 and l are connected forenergizing any load X which is to be energized by direct current of ahigher voltage than available from the direct current service lines LIand L2.

Upon each circumferential path of each of said drums bear the sixbrushes previously referred to, which are connected as three pairs ofbrushes as shown; the centers of brushes of the same pair are spaced ata distance equal to the distance between the centers of two adjacentcontact-segments of opposite polarity; each pair of brushes with respectto the others in the same path is set up in advance 120 electricaldegrees. The relative position of brushes is shown by the hatchedsquares I'II. Each pair of brushes of the small drum is in circuit withthe primary of one of the transformer coils as shown at AH, BH and CH,also the corresponding pair of brushes of the large drum is in circuitwith the secondary of the same transformer coil.

The operation of this system of direct-current transformation is asfollows: The primary direct-current is supplied to slip-rings 4B and 5Bof the rotating converter-rectifier which are connected with therespective contact-segments. By

phase alternating current. Only three of said circuits are shown for thesake of clearness. For example, a pair ofbrushes 23A24A which begins tocome in contact with the positive-neg ative pair of adjacentcontact-segments will gradually increase the contact area and thecurrent density in the AH branch circuit until they attain a maximum atthe center of the segment, then the contact area will graduallydecrease, decreasing the current density until the brushes attain aneutral position between the segments, thus making a positive half of acycle, or 180 electrical degrees. Thereupon both said brushes begincontacting the next pair'of segments which is negative-positive, so thecurrent in said branch circuit is reversed, repeating the increase, themaximum, the decrease and the neutral position and. completing thenegative half of the cycle. These halves-of the current cycle passingthrough the primary winding AH induce in the secondary winding AL thehalves of transformed current cycles in opposite directions. Theconnections with the segments of converting drum and the connections.with the "segments of rectifying drum with their respective inductioncoils being changed'or advanced simultaneously, the negative half of thesecondary cycle is always supplied to the positive segment of therectify-.

ing drum and the positive half of the same cycle to the negativesegment. Also all the successive half cycles of alternations in variousphases are fed to segments of the proper polarity of the rectifying drumand to its slip-rings 4-5 from which the direct current of a changedvoltage is collected by the brushes 6-1 of the secondary direct-currentline. Since the contact segments of like polarity enter in contact withthe brushes gradually, one contact beginning while the others are incontinuation and since a number of circuits is always in contact withrespective segments, the primary and the secondary directcurrents arekept uninterrupted, though in the parallel branches the current is madealternating. For the same reason the current density in the individualcontact-segments remains low and unchanged although the contact areawith a particular brush is gradually decreasing until the contact ceasesentirely, inasmuch as a free path for the current is provided in thecopper of several other circuits continuing at the instant grease;

of the contact with respective pairs of brushes. The current havingseveral free paths in the copper would not jump through the airfollowing the brushes changing the segments.

Thus the excessive sparking in this apparatus is prevented by theprovision of a free and uninterrupted path for the currentin the copperof a number of acting circuits.

The direct current changer may be designed to operate on a smaller orgreater number of phases, but the larger number of phases is moreeffective because this operates to decrease the heating of the device,increasing its capacity. The capacity of such current changers islimited generally by the temperatures to which the various parts may beallowed to rise with safety. The decrease in heating is directlyproportional to the difference between the square of the main currentand the sum of the squares of currents. flowing in the parallelbranches. Thus the larger number of phases makes possible a greatercapacity for a given size of unit.

In Figures 5 and 6 I have shown an embodiment comprising only two ofthe'cylindrical electrically conductive elements I and 2 mounted inconcentric spaced apart relation on a rotatable shaft 3. As in theprevious embodiments, one of the cylindrical elements 2 is of smallerdiameter and being longer axially it projects from both ends of theshorter but larger element. Two adjacent ends of the cylindricalelements I and 2 carry annular flanges F in axially spaced relation andcontact segments 8 and 9 project therebetween in circumferential equallyspaced relation for defining a contact drum, as in the previouslydescribed embodiment. a

A pair of slip rings 4 and 5 is similarly supported in axially spacedrelation from the opposite ends of the elements I and 2 for engagingbrushes (not shown). An intermediate contact drum is formed by anannular flange F" carried on an intermediate portion of the. cylindricalelement I to which it may be secured in any suit- (not shown) arrangedin two sets, as for dividing alternating current to a greater number ofphases and the like. The size and spacing of the contact segments isarranged with proper con- The contact segments I8 are divided tosideration of the voltage and current to be applied therethrough andeach brush engaging area is of a tapered conformation at its leading andlagging ends. The frequency is determined by the speed at which thecommutator is rotated, and the number and angular spacing of the contactsegments provided. k

By disposing suitable sets of brushes engaging the end contact drum andthe intermediate contact drum, the simplified construction of Figures 5and 6, may be conveniently utilized for various purposes such aschanging a two-phase current of a certain voltage, frequency andamplitude to a three-phase or to a six-phase current of a differentvoltage frequency,-and amplitude and vice versa; as will be readilyunderstood. Also by utilizing the slip rings for direct currentconnection, this simplified device can be utilized for converting directcurrent to alternating current of various frequencies, and vice versa.The number'of contact segments provided, and the speed at which theshaft 3 is rotated bears a predetermined relation to the frequency ofthe alternating current which is to be inverted, converted ortransformed, which will be readily understood.

,For certain purposes the intermediate contact drum I8 is unnecessaryand may be omitted thus providing a. simplified construction consistingonly of the pair of cylindrical elements I and 2, having the pair ofslip rings at one end, and a single circular path of contact segments.This simplified arrangement is sufficient to accomplish the purpose ofchanging direct current to alternating current, or vice versa, as willbe readily understood.

-It is obvious that various modifications may be made both in theapparatus and circuit connections herein shown and described, withoutdeparting from the principle of my invention, and

7 those which are shown are only examples exconverter-rectifier.

plaining the various modes of use of the samel. A commutator formechanical polyphase converters comprising, a shaft, a pair ofelectrically conductive cylindrical elements of different diametersdisposed in insulated concentric relation on said shaft, the cylindricalelement of smallest diameter being longest in axial length for extendingat one end beyond one end of the short cylindrical element, a pair ofslip rings' different diameters disposed in concentric relaa 'tion onsaid shaft, the cylindrical element of smallest diameter being longestfor extending beyond the ends of the short cylindrical element, a pairof slip rings of substantially equal diameters disposed on adjacent endsof said cylindrical elements in axially spaced relation for continuouslyengaging a pair of axially spaced brushes, contact segments extendingfrom the other end of one of said cylinders in a circular path aroundthe commutator, and contact segments extending from the adjacent end ofthe other one of said cylinders in alternately spaced relation betweensaid first mentioned contact segments.

3. A-commutator for a mechanical polyphase converter comprising, ashaft, a pair of cylindrical metallic elements of different diametersdisposed in insulated concentric relation on said shaft, thecylindricalelement of smallest diameter being longest for extendingbeyond the ends of the short cylindrical element, a pair of slip ringsdisposed on adjacent ends of said cylindrical 7 elements for brushes,spaced annular flanges projecting laterally from the other axiallyspaced ends of said pair of cylinders, and contact segments projectingfrom the outerrims of said flanges respectively in alternately spacedrelation to define a contact drum for engaging a plurality of spacedbrushes.

'4. A commutator for a mechanical direct current transformer comprising,a shaft, four eleccontinuously engaging s,

trically conductive cylindrical elements of different diameters disposedin insulated concentric relation on said shaft, said cylindricalelements being of different lengths with the longest cylindricalelements adjacent said shaft and project ing progressively beyond theencircling elements, slip rings supported on the ends of saidcylindrical elements projecting progressively toward one end of theshaft, contact segments extending from the other ends of the larger pairof cylinders in alternately spaced relation defining a circumferentialpath around the commutator for engaging a plurality of brushes, andcontact segments extending from the other ends of the smaller pair ofcylinders in alternately spaced relation defining a circumferential patharound the commutator in axially off-set relation from the firstmentioned path for engaging'a second set of brushes.

5. A commutator for a mechanical direct current transformer comprising,a shaft, four electrical ly conductive cylindrical elements of differentdiameters disposed in insulated concentric relation on said shaft, saidcylindrical elements being of different lengths arranged inprogressively projecting relation with the longest cylindrical elementadjacent said shaft, slip rings supported on the ends of the cylindricalelements which project progressively toward one end of the shaft, fourspaced annular flanges projecting respectively fromthe other axiallyspaced ends of said cylindrical elements in two pairs of substantiallyequal diameters, and contact segments projecting from the respectiverims of said pairs of flanges in alternately spaced relation to definetwo contact drums for engaging a plurality of spaced brushes.

6. A commutator for a mechanical polyphase converter comprising, ashaft, a pair of metallic elements of cylindrical conformation havingdifferent lengths and diameters, said elements being mounted ininsulated concentric relation on said shaft with the longest elementdisposed next adjacent the shaft, a pair of slip rings disposed onunequally extended ends of said cylindrical elements for continuouslyengaging brushes of different polarity, contact segments extending fromthe other end of one of said cylindrical elements in a circular patharound the commutator'contact segments "extending from the adjacent endof the other one of said cylindrical elements in alternately spacedrelation between the first mentioned contact segments to define acontact drum for engaging a plurality of spaced brushes, and each one ofsaid contact segments having a contact surface of a conformationtapering on both the leading and the lagging extremities thereof.

7. A commutator for a mechanical polyphase converter comprising, ashaft, a pair of metallic elements of cylindrical conformation havingdifferent lengths and diameters, said elements being mounted ininsulated concentric relation on said shaft with the longest elementdisposed next adjacent the shaft, 2. pair of slip rings disposed onunequally extended ends of said cylindrical elements for continuouslyengaging brushes of different polarity, contact segments extending fromthe other end of one of said cylindrical elements in a circular patharound the commutator, a

- plurality of contact areas on each one of said contact'segmentsfordefining a plurality of circumferential paths around the commutatoras it rotates, contact segments extending from the adjacent end of theother one of said cylinders in alternately spaced relation between thefirst mentioned contact segments, a plurality of contact areas on eachone of the contact segments ex-, tending from said other one of saidcylinders, said second mentioned contact areas being disposed in axialalignment with the first mentioned contact areas whereby a plurality ofcircumferential paths are described as the commutator rotates 10 forcontacting a plurality of sets of spaced brushes aromas and thusdividing the current from the commutatorr it. A commutator for amechanical polyphase converter comprising the combination defined inclaim 7; in which each one of the contact areas is of a sizeproportional to the size of the brushes to be used, and each contactarea has a contact surface of a conformation tapering on both theleading and the lagging extremities thereof.

' MICHAEL I. TOPALOV.

